Giardia lamblia is a parasite protozoa and a primitive eukaryote, is responsible for water born enteric infection throughout tropical and temperate zones. The mechanism by which this organism causes diarrhea is currently unknown. It has been postulated that surface antigens of this parasite play an important role during the host-parasite interactions. Recently, we have found an invariant antigen on the surface of Giardia, which is stable and present in different isolates (GP49). GP49 is linked to the outer surface of the plasma membrane with a novel Glycophospholipid anchor and secreted in the culture medium. It has been documented previously that the enzyme PI-PLC is responsible for the cleavage of the Glycophospholipid (GPI) anchored surface antigens of the parasitic protozoa and other eukaryotes. Although the biological function of GP49 is not known, recently we found that intact and soluble GP49 altered the electrolyte fluxes which regulate fluid secretion in the cultured human intestinal epithelial cell line, T84. Therefore it can be postulated that the enzyme, phosphatidylinositol specific phospholipase-C(PI-PLC) of Giardia is responsible for the cleavage and the secretion of GP49. Here we propose to study PI-PLC from G. Lamblia using biochemical and molecular methodologies for the first time.